Hybrid powertrain systems are defined as having more than one source of power to accomplish the task of propelling and accelerating an automotive vehicle. Dividing an engine into independently operating modules accomplishes this task, without the cost, complication, and inefficiency of storing and converting energy such as is done with other hybrid systems such as electric hybrids. An engine having independent modules overcomes the major causes of inefficiency by allowing the independent operation of two, four, or six cylinders in a six cylinder engine.
The important considerations in the design of a modular engine include the following. Optimizing fuel efficiency factors such as maximizing thermal efficiency and reducing mechanical friction. Meeting emission targets from the combustion chamber and proper treatment of exhaust gases. Smoothing the torque pulses from the cylinder firing with a low number of operating cylinders or an unconventional firing sequence. Coping with primary and higher order unbalance forces by positioning of the cylinders and use of auxiliary balancing schemes. Meeting cost and mass targets. Being compatible with the latest industry technology breakthroughs such as free breathing, variable valve timing, new materials, and closed loop fuel and ignition controls.
Two stroke engine technology is attractive for a modular engine having separate modules because the one-per-revolution firing frequency smooths torque pulses for a two cylinder operating module. Cylinder ports for controlling the opening of air inlet and exhaust outlet passages greatly simplifies engine construction by eliminating much or all of the conventional valve gear. However, optimizing fuel efficiency and emissions possibly requires some form of variable valve timing, so some controllable augmentation to the port opening timing may be needed through rotary or poppit valves. These valves are actuated mechanically, electrically, or electro-hydraulically.
A modular engine consists of separate engine modules. Each module includes at least one cylinder with a piston and a connecting rod attached to a crankshaft segment. Each crankshaft segment of a module is connected to a crankshaft segment of another engine module by a clutch. The clutch is typically a one way clutch generally referred to as a mechanical diode.
The clutch allows angular indexing of the crankshaft segments and the engine modules to a specific angular position to minimize torque pulses. For instance, an engine may have first and second engine modules with each engine module having two cylinders. To convert from a two cylinder even firing engine module at 180.degree. firing intervals to a four cylinder even firing engine module pair at 90.degree. firing intervals, the crankshaft segments of each of the two engine modules have to be linked to index the crankshaft segments at 90.degree. rotation intervals.
A problem is that to add a third engine module to the previous two engine modules, it is necessary to have the firing intervals be at 60.degree. between the three engine modules. However, the crankshaft segment of the third engine module is linked to the crankshaft segment of a second engine module to index the second and third crankshaft segments at 90.degree. rotation intervals to provide even firing when the second and third engine modules are operable and the first module is inoperable. In the above described scenario, first and second engine modules provide proper firing when the third engine module is inoperable because their crankshaft segments are at 90.degree. rotation intervals. Second and third engine modules provide proper firing when the first engine module is inoperable because their crankshaft segments are at 90.degree. rotation intervals. However, first, second, and third engine modules provide improper firing when they are all operable because their crankshaft segments are not at 60.degree. rotation intervals.
A similar condition exists with four stroke engines except that firing intervals are 360.degree. for a two cylinder engine, 180.degree. for a four cylinder engine, and 120.degree. for a six cylinder engine. What is needed is a modular engine having at least three engine modules in which the crankshaft segments of the engine modules are connected by a torsion spring to provide even firing between the engine modules.